A hormone produces its effect by binding to a target cell’s receptors for that hormone. The more receptors it binds to, the greater is the effect on the target cell. All hormones affect target cells by altering their metabolic activities. For example, they may change the rate of cellular processes in general, or they may promote or inhibit specific cellular processes. The end result is that homeostasis is maintained.
Mechanisms of Action of Steroid And Non steroid Hormones
Steroid And Thyroid Hormones
Steroid hormones and thyroid hormones act on DNA in a cell’s nucleus and affect gene expression.
1. Because they are lipid-soluble, they can easily move through the phospholipid bilayers of plasma membranes to
2. enter the nucleus.
3. After a hormone enters the nucleus, it combines with an intracellular receptor to form a hormone-receptor complex.
4. The hormone-receptor complex interacts with DNA, activating specific genes that synthesize messenger RNA (mRNA). 5 The mRNA exits the nucleus and interacts with ribosomes, which results in the synthesis of specific proteins, usually enzymes. Then the newly formed proteins produce the specific effect that is characteristic of the particular hormone.
Non steroid Hormones
Nonsteroid hormones are proteins, peptides, or modified amino acids that are not lipid-soluble, meaning they cannot pass across the phospholipid bilayer. Two messengers are required for these hormones to produce their effect on a target cell. The first messenger is the nonsteroid hormone bound to a receptor on the plasma membrane. The first messenger leads to the formation of a second messenger that is often, but not always, cyclic adenosine monophosphate (cAMP). The second messenger is formed within the cell, and it activates or inactivates enzymes that produce the characteristic effect for the hormone. When a cAMP is the second messenger, the sequence of events is as follows.
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